Effect of the Pipe Bend of the Morning Glory Spillway on the Cavitation Number

Abstract

Present study carried out a series experimental tests to validate a numerical model of the morning glory spillway with different R/D ratio (diameter size of the vertical and horizontal shaft divided with radius of the bend pipe). The cavitation numbers over the morning glory spillway were determined for different flow conditions as the free, semi submerged and submerged flow by employing the validated numerical models. The cavitation values of the free flow condition showed that cavitation was mainly occurred on the internal arch of the bend pipe; however, it seems that the external arch has never faced by cavitation. Results of the semi-submerged flow condition showed that the level of the danger was the major danger level for internal arch of the bend pipe which seems that this position obtains the high danger of the cavitation. The results of the submerged flow condition indicates that the crest level at the entrance of the morning glory spillway was additionally threated by cavitation; however, the bend pipe position was suffered from the high cavitation values, the fully pipe flow reduce the minus values of the static pressure and it causes that the cavitation danger risk was decreased compared by semi-submerged condition. Finally, to prevent from the cavitation, the values of the cavitation number due to different R/D as 0.55, 0.45, 0.35, and 0.25 were calculated by employing the validated numerical model due to high danger of the cavitation based on the flow condition which was semi-submerged condition. Results showed that due to D/R <0.35, the possible cavitation damage is obtained for the internal and external arch of the bend pipe of the morning glory spillway; however, for D/R <0.25, the bend pipe position is located in safe zone and the danger of the cavitation is negligible..

Keywords: cavitation number, velocity, static pressure, pipe diameter, bend radius.